Mask for extreme ultraviolet photolithography

ABSTRACT

A method for forming an extreme ultraviolet photolithography mask includes forming a reflective multilayer, forming a buffer layer on the reflective multilayer, and forming an absorption layer on the reflective multilayer. Prior to patterning the absorption layer, an outer portion of the absorption layer is removed. Photoresist is then deposited on the top surface of the absorption layer and on sidewalls of the absorption layer. The photoresist is then patterned, and the absorption layer is etched with a plasma etching process in the presence of the patterned photoresist. The presence of the photoresist on the sidewalls of the absorption layer during the plasma etching process helps to improve uniformity in the etching of the absorption layer during the plasma etching process.

BACKGROUND Technical Field

The present disclosure relates to the field of photolithography. Thepresent disclosure relates more particularly to forming masks forphotolithography processes.

Description of the Related Art

The semiconductor integrated circuit industry has experiencedexponential growth. Technological advances in integrated circuitmaterials and design have produced generations of integrated circuits inwhich each generation has smaller and more complex circuits than theprevious generation. In the course of integrated circuit evolution, thenumber of interconnected devices per chip area has generally increasedwhile the sizes of the smallest components that can be created using afabrication process has decreased.

This scaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs. Such scaling downhas also increases the complexity of integrated circuit processing andmanufacturing. For these advances to be realized, similar developmentsin integrated circuit processing and manufacturing are needed. Forexample, the need to perform higher resolution photolithographyprocesses grows.

Extreme ultraviolet photolithography is photolithography process thatemploys scanners using light in the extreme ultraviolet region havingwavelengths of about 1-20 nm. Extreme ultraviolet scanners provide adesired pattern on an absorption layer formed on a reflective mask. Thepattern of the absorption layer is utilized to form features on asemiconductor wafer based on the pattern.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an extreme ultraviolet photolithographysystem, according to one embodiment.

FIG. 2 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 3 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 4A is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 4B is a top view of the photolithography mask of FIG. 4A, accordingto one embodiment.

FIG. 5 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 6 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 7 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 8 is a cross-sectional view of a photolithography mask, accordingto one embodiment.

FIG. 9 is a cross-sectional view of a photolithography mask at anintermediate stage of processing, according to one embodiment.

FIG. 10 is a flow diagram of a method for forming a photolithographymask, according to one embodiment.

FIG. 11 is a flow diagram of a method for forming a photolithographymask, according to one embodiment.

DETAILED DESCRIPTION

In the following description, many thicknesses and materials aredescribed for various layers and structures within a photolithographymask. Specific dimensions and materials are given by way of example forvarious embodiments. Those of skill in the art will recognize, in lightof the present disclosure, that other dimensions and materials can beused in many cases without departing from the scope of the presentdisclosure.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the described subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present description. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

FIG. 1 is a block diagram of an extreme ultraviolet photolithographysystem 100, according to one embodiment. The system includes a radiationsource 102, an illuminator 104, a mask 106, a projection optics box 108,and a target 110. The components of the system 100 cooperate together toperform extreme ultraviolet photolithography processes.

The radiation source 102 outputs ultraviolet radiation. The ultravioletradiation has a wavelength of about 1-20 nm. The ultraviolet radiationmay include other wavelengths without departing from the scope of thepresent disclosure.

The illuminator 104 receives the ultraviolet radiation from theradiation source. The illuminator 104 may include refractive optics,such as a single lens or a lens system having multiple lenses (zoneplates) and/or reflective optics, such as a single mirror or a mirrorsystem having multiple mirrors. The illuminator directs ultravioletradiation from the radiation source 102 onto the mask 106.

The mask 106 receives the ultraviolet radiation from the illuminator104. The mask 106 can be a transmissive mask or a reflective mask. Inone embodiment, the mask 106 is a reflective mask such as described infurther detail below. The mask 106 may incorporate other resolutionenhancement techniques such as phase-shifting mask (phase-shifting mask)and/or optical proximity correction (optical proximity correction).

The projection optics box 108 receives the ultraviolet radiation fromthe mask 106. The projection optics box 108 may have refractive opticsor reflective optics. The radiation reflected from the mask 106 (e.g., apatterned radiation) is collected by the projection optics box 108. Theprojection optics box 108 may include a magnification less than one(thereby reducing the patterned image included in the radiation). Theprojection optics box directs the ultraviolet radiation onto the target110.

In one embodiment, the target 110 includes a semiconductor wafer. Alayer of photoresist typically covers the target during extremeultraviolet photolithography irradiation. The photoresist assists inpatterning a surface of the semiconductor wafer in accordance with thepattern of the mask 106.

The projection optics box 108 focuses the extreme ultraviolet light ontothe target 110. The extreme ultraviolet light irradiates the photoresistwith a pattern corresponding to the pattern of the mask 106. The exposedportions of the photoresist undergo a chemical change that enablesportions of the photoresist to be removed. This pattern leavesphotoresist on the surface of the semiconductor wafer in a pattern ofthe mask 106. Etching processes, thin film deposition processes, and/ordoping processes are performed in the presence of the patternedphotoresist.

Typically, a large number of masks 106 are utilized during fabricationof a single semiconductor wafer. Each mask has a particular patterncorresponding to semiconductor fabrication processes. One or moreetching, deposition, or doping processes are performed in accordancewith each mask.

If there are defects in the mask 106, then corresponding defects mayoccur in the various semiconductor processes associated with the mask106. The defects that propagate from the mask 106 to the fabricationprocesses can result in semiconductor devices that do not functionproperly. Semiconductor devices that do not function properly representa waste of large amounts of resources due to the large amount of time,expensive tools, and expensive materials required to fabricate eachsemiconductor device. Accordingly, it is beneficial to reduce as many asdefects in the mask 106.

The photolithography system 100 described in relation to FIG. 1 is oneexample of some components of a photolithography system. Aphotolithography system can include other components, processes, andconfigurations than those described above without departing from thescope of the present disclosure.

FIG. 2 is a cross-section of an extreme ultraviolet photolithographymask 106 during an intermediate stage of processing, according to oneembodiment. The mask 106 includes a substrate 112, a reflectivemultilayer 114 positioned on the substrate 112, a buffer layer 116positioned on the reflective multilayer 114, and an absorption layer 118positioned on the buffer layer 116. The fabrication process of the mask106 eventually results in the mask 106 having a selected pattern in theabsorption layer 118.

The substrate 112 includes a low thermal expansion material. The lowthermal expansion material substrate 112 serves to minimize imagedistortion due to heating of the mask 106. The low thermal expansionmaterial substrate 112 can include materials with a low defect level anda smooth surface.

In one embodiment, the substrate 112 can include SiO₂. The substrate 112can be doped with titanium dioxide. The substrate 112 can include otherlow thermal expansion materials than those described above withoutdeparting from the scope of the present disclosure.

Though not shown herein, in one embodiment the substrate 112 may bepositioned on a conductive layer. The conductive layer can assist inelectrostatically chucking the mask 106 during fabrication and use ofthe mask 106. In one embodiment, the conductive layer includes chromiumnitride. The conductive layer can include other materials withoutdeparting from the scope of the present disclosure.

The mask 106 includes the reflective multilayer 114. The reflectivemultilayer 114 is positioned on the substrate 112. The reflectivemultilayer 114 is configured to reflect the extreme ultraviolet lightduring photolithography processes in which the mask 106 is used. Thereflective properties of the reflective multilayer 114 are described inmore detail below.

In one embodiment, the reflective multilayer 114 operates in accordancewith reflective properties of the interface between two materials. Inparticular, reflection of light will occur when light is incident at theinterface between two materials of different refractive indices. Agreater portion of the light is reflected when the difference inrefractive indices is larger.

One technique to increase the proportion of reflected light is toinclude a plurality of interfaces by depositing a multilayer ofalternating materials. The properties and dimensions of the materialscan be selected so that constructive interference occurs with lightreflected from different interfaces. However, the absorption propertiesof the employed materials for the plurality of layers may limit thereflectivity that can be achieved.

Accordingly, the reflective multilayer 114 includes a plurality of pairsof layers. Each pair of layers includes a layer of a first material anda layer of a second material. The materials and thicknesses of thelayers are selected to promote reflection and constructive interferenceof extreme ultraviolet light.

In one embodiment, each pair of layers includes a layer of molybdenumand a layer of silicon. In one example, the layer of molybdenum isbetween 2 nm and 4 nm in thickness. In one example, the layer of siliconis between 3 nm and 5 nm in thickness. The thicknesses of the layers inthe reflective multilayer 114 are selected based on the expectedwavelength of extreme ultraviolet light used in the photolithographyprocesses and the expected angle of incidence of the extreme ultravioletlight during the photolithography processes. The wavelength of theextreme ultraviolet light is between 1 nm and 20 nm. The number of pairsof layers is between 20 pairs of layers and 60 pairs of layers,according to one embodiment. Other materials, thicknesses, numbers ofpairs, and configurations of layers in the reflective multilayer 114 canbe utilized without departing from the scope of the present disclosure.Other wavelengths of extreme ultraviolet light can be used withoutdeparting from the scope of the present disclosure.

In one embodiment, the buffer layer 116 is positioned on the reflectivemultilayer 114. One purpose of the buffer layer 116 is to protect thereflective multilayer during etching processes of the absorption layer118. Accordingly, the buffer layer 116 includes materials that areresistant to etching by etching processes that etch the absorption layer118. The etching processes and the materials of the absorption layerwill be described in more detail below.

In one embodiment, the buffer layer 116 includes ruthenium. The bufferlayer 116 can include compounds of ruthenium including ruthenium borideand ruthenium silicide. The buffer layer can include chromium, chromiumoxide, or chromium nitride. The buffer layer 116 can be deposited by alow temperature deposition process to prevent diffusion of the bufferlayer 116 into the reflective multilayer 114. In one embodiment, thebuffer layer 116 has a thickness between 2 nm and 4 nm. Other materials,deposition processes, and thicknesses can be utilized for the bufferlayer 116 without departing from the scope of the present disclosure.

The absorption layer 118 is positioned on the buffer layer 116. Thematerial of the absorption layer 118 is selected to have a highabsorption coefficient for wavelengths of extreme ultraviolet radiationthat will be used in the photolithography processes with the mask 106.In other words, the materials of the absorption layer 118 are selectedto absorb extreme ultraviolet radiation.

In one embodiment, the absorption layer 118 is between 40 nm and 100 nmin thickness. In one embodiment, the absorption layer 118 includesmaterial selected from a group including chromium, chromium oxide,titanium nitride, tantalum nitride, tantalum, titanium, aluminum-copper,palladium, tantalum boron nitride, tantalum boron oxide, aluminum oxide,molybdenum, or other suitable materials. Other materials and thicknessescan be used for the absorption layer 118 without departing from thescope of the present disclosure.

In one embodiment, the absorption layer 118 includes a first absorptionlayer 120 and a second absorption layer 122. The first absorption layer118 is positioned on the buffer layer 116. The second absorption layer122 is positioned on the first absorption layer 120.

In one embodiment, the first absorption layer 120 includes tantalumboron nitride. The second absorption layer 122 includes tantalum boronoxide. The thickness of the first absorption layer is between 30 nm and80 nm. The thickness of the second absorption layer 122 is between 1 nmand 40 nm. The absorption layer 118 can include different materials,thicknesses, and numbers of layers than those described above withoutdeparting from the scope of the present disclosure. In one embodiment,the absorption layer 118 includes only a single absorption layer.Accordingly, the absorption layer 118 can be an absorption layer.

The layers of the mask 106 shown in FIG. 2 may be formed by variousthin-film deposition processes. The thin-film deposition processes caninclude including physical vapor deposition process such as evaporationand DC magnetron sputtering, a plating process such as electrolessplating or electroplating, a chemical vapor deposition process such asatmospheric pressure chemical vapor deposition, low pressure chemicalvapor deposition, plasma enhanced chemical vapor deposition, highdensity plasma chemical vapor deposition, ion beam deposition, spin-oncoating, metal-organic decomposition, and/or other methods known in theart.

FIG. 3 is a cross-section of a photolithography mask 106 at anintermediate stage of processing, according to one embodiment. In FIG.3, a layer of photoresist 124 has been deposited on the absorption layer118. In particular, the layer of photoresist 124 has been deposited onthe second absorption layer 122. The layer of photoresist 124 has beenpatterned and developed to expose an outer edge of the top surface ofthe absorption layer 118.

The layer of photoresist 124 can be patterned using commonphotolithography techniques including exposing the photoresist 124 tolight or e-beam processes through a photolithography mask and developingthe photoresist to remove the outer perimeter of the photoresist 124 inaccordance with a pattern of the photolithography mask.

In one embodiment, the width of the exposed portion of the top surfaceof the absorption layer 122 is between 0.2 mm and 2 mm. In other words,the edge of the photoresist 124 is between 0.2 mm and 2 mm from the edgeof the absorption layer 118. Though not shown in FIG. 3, the mask 106may be substantially rectangular from a top view. The exposed portion ofthe absorption layer 118 corresponds to an outer edge of the rectangle.Those of skill in the art will recognize, in light of the presentdisclosure that the exposed portion of the absorption layer 118 can haveother dimensions and shapes, without departing from the scope of thepresent disclosure. For example, other widths are possible for theexposed portion of the top surface of the absorption layer 122 withoutdeparting from the scope of the present disclosure. For example, inother embodiments, the width of the exposed portion of the top surfaceof the absorption layer 122 is between 0.2 mm to 3 mm.

FIG. 4A is a cross-section of the mask 106 at an intermediate stage ofprocessing, according to one embodiment. In the illustrated embodimentof FIG. 4A, an outer portion of the absorption layer 118 has beenremoved. The outer portion of the absorption layer 118 can be removed byan etching process in the presence of the patterned photoresist 124. Thephotoresist 124 is then removed. The result of the etching process isthat an outer portion 126 of the top surface of the buffer layer 116 isexposed. The exposed portion corresponds to the pattern of thephotoresist 124 in FIG. 3. The exposed portion 126 is between 0.2 mm and2 mm in width. The exposed portion 126 extends around the perimeter ofthe mask 106. The exposed portion 126 should be wide enough to enablephotoresist to stably cover the sidewalls of the absorption layer, forreasons that will be set forth in more detail below. The exposed portion126 should be narrow enough to enable full patterning of the absorptionlayer in accordance with a selected pattern for the mask 106 to be usedin extreme ultraviolet photolithography processes. Accordingly, therange of values can be selected based, in part, on the particular typeof photoresist to be used in patterning the absorption layer.

In one embodiment, the etching process may include dry plasma etching,wet etching, and/or other etching methods. In the present embodiment, amultiple-step dry etching is implemented. In one embodiment, the etchingprocess can include a two-step plasma etching process. The secondabsorption layer 122 can be etched with a first plasma etching process.The first absorption layer 120 can be etched with a second plasmaetching process.

Those of skill in the art will recognize, in light of the presentdisclosure, that other processes than those described in relation toFIG. 3 and FIG. 4A can be utilized to form a mask having a pattern inaccordance with FIG. 4A without departing from the scope of the presentdisclosure.

FIG. 4B is a top view of the photolithography mask 106 of FIG. 4A,according to one embodiment. In the view of FIG. 4B, the absorptionlayer 118 is positioned on the buffer layer 116. The absorption layer118 does not entirely cover the top surface of the buffer layer 116. Anouter portion 126 of the top surface of the buffer layer 116 is notcovered by the absorption layer. The width W of the exposed portion 126of the top surface of the buffer layer 116 is between 0.2 mm and 2 mm.Other widths are possible for the exposed portion 126 without departingfrom the scope of the present disclosure. For example, in accordancewith other embodiments of the present disclosure, the width W of theexposed portion 126 of the top surface of the buffer layer 116 isbetween 0.2 mm to 3 mm. Although the width W of the exposed portion 126is shown as being the same on all sides of the photolithography mask 106in FIG. 4B, in some embodiments the exposed portion 126 may havediffering widths on different sides of the photolithography mask 106.

In one embodiment, a lateral width of the absorption layer 118 issmaller than a lateral width of the buffer layer 116. In one embodiment,an outer perimeter of the top surface of the buffer layer 116 is exposedby the absorption layer 118 because the absorption layer 118 does notcover the outer perimeter of the top surface of the buffer layer 116. Inone embodiment, the exposed portion 126 has the shape of a framesurrounding the absorption layer 118. The mask 106 is substantiallyrectangular, though other shapes are possible for the mask 106 withoutdeparting from the scope of the present disclosure.

FIG. 5 is a cross-section of the photolithography mask 106 at anintermediate stage of processing, according to one embodiment. In FIG.5, a layer of photoresist 128 has been deposited on the absorption layer118. The photoresist 118 is positioned on a top surface of theabsorption layer 118, on lateral surfaces of the absorption layer 118,and on the exposed portion 126 of the buffer layer 116. The photoresist128 is utilized to assist in patterning the absorption layer 118 inaccordance with a final pattern of the mask 106. As will be described inmore detail below, several benefits result from removing an outerperimeter of the absorption layer 118 such that the photoresist 128covers the lateral surfaces of the absorption layer 118.

FIG. 6 is a cross-section of the photolithography mask 106, according toone embodiment. In FIG. 6, the photoresist 128 has been patterned. Thepatterning results in trenches 130 formed in the photoresist 128.Portions of the top surface of the absorption layer 118 are exposed viathe trenches 130 formed in the photoresist 128.

In one embodiment, the trenches 130 are formed in the photoresist 128 byexposing the photoresist 128 to an e-beam process through a mask. Thepatterning can include exposing the photoresist to an e-beam process,baking the photoresist 128, and developing the photoresist 128, leavingthe pattern of trenches 130 in the photoresist 128. Those of skill inthe art will recognize, in light of the present disclosure, that manytypes of photolithography and patterning processes can be utilized topattern the photoresist 128 as shown in FIG. 6.

FIG. 7 is a cross-section of the photolithography mask 106 at anintermediate stage of processing, according to one embodiment. The mask106 has been subjected to an etching process. The etching process ofFIG. 7 etches the exposed portions of the absorption layer 118 via thetrenches 130 in the photoresist 128. The result of the etching processis that the absorption layer 118 is etched in accordance with thepattern of the photoresist 128 in FIG. 6. The etching process leavestrenches 134 in the absorption layer 118 in the pattern of thephotoresist 128.

In one embodiment, the etching process stops at the buffer layer 116.Accordingly, the top surface of buffer layer 116 is exposed through thetrenches 134 in the photoresist 128. The etching process for theabsorption layer 118 is selected so that the absorption layer 118 isselectively etched with respect to the buffer layer 116. Accordingly,the buffer layer 116 is not etched by the process that etches theabsorption layer 118.

In one embodiment, the etching process for the absorption layer 118 is aplasma etching process. The plasma etching process includes generating aplasma with a chlorine-based gas. The chlorine gas plasma etchingprocess selectively etches the absorption layer 118 with respect to thebuffer layer 116. In one embodiment, the plasma etching process canstart with a fluorine gas plasma to etch the second absorption layer122. The plasma etching process can then switch to a chlorine gas plasmato etch the first absorption layer 120. Other types of etching processescan be utilized without departing from the scope of the presentdisclosure.

FIG. 8 is a cross-section of the mask 106, according to one embodiment.In the view of FIG. 8, the photoresist 128 has been removed. Theabsorption layer 118 remains patterned with trenches 134. The topsurface of the buffer layer 116 is exposed through the trenches 134 inthe absorption layer 118 and along an outer perimeter of the mask 106.

Some of the benefits of the mask fabrication process shown in relationto FIGS. 2-8 are illustrated by comparison with a different process formask fabrication shown in relation to FIG. 9.

FIG. 9 is a cross-section of a photolithography mask 140 at anintermediate stage of processing, according to one embodiment. Thephotolithography mask 140 includes a substrate 112, a reflectionmultilayer 114, a buffer layer 116, and an absorption layer 118. Apatterned layer of photoresist 128 covers the absorption layer 118.Trenches 134 have been etched in the absorption layer 118 in accordancewith the patterned photoresist 128.

The photolithography mask 140 of FIG. 9 is similar in many regards tothe photolithography mask 106 of FIG. 7. However, one difference betweenthe photolithography mask 140 and the photolithography mask 106 of FIG.7 is that in the mask 140 the photoresist 128 does not cover the lateralsurfaces of the absorption layer 118 in FIG. 9. This is because theabsorption layer 118 of the mask 140 has not been patterned to exposethe outer perimeter of the buffer layer 116, unlike the mask 106. Inparticular, the photolithography processes of FIGS. 3 and 4A etched anouter perimeter of the absorption layer 118, exposing a portion 126 ofthe top surface of the buffer layer 116. One of the results of thephotolithography processes shown in FIGS. 3 and 4A is that thephotoresist 128 in FIGS. 5-7 covers the lateral surfaces of theabsorption layer 118 of the mask 106.

Accordingly, during the plasma etch process described in relation toFIG. 7 for forming the trenches 134 in the absorption layer 118 of themask 106, the lateral surfaces of the absorption layer 118 are coveredby the photoresist 128. The photoresist 128 of the mask 140 of FIG. 9does not cover the lateral surfaces of the absorption layer 118.Accordingly, the lateral surfaces of the absorption layer 118 of themask 140 are exposed during the plasma etching process for etching thetrenches 134.

The absorption layer 118 is relatively conductive compared to thereflective multilayer 114 in the substrate 112. If the lateral surfacesof the absorption layer are exposed during the plasma etch, relativelyhigh voltage differences may develop between different areas of the topsurface of the absorption layer 118 during the plasma etching process.The result is that the plasma etches at a faster rate at different areasof the absorption layer 118 during the plasma etching process.

Different etching rates at different areas of the absorption layer 118result in disparities between the trenches 134 at different parts of theabsorption layer 118. This in turn leads to site to site differenceswhen processing semiconductor wafers using the mask 140. The site thesite differences can cause some areas of the semiconductor wafers tohave defects. These defects may result in some of the integratedcircuits that result from the semiconductor wafers being nonfunctioning.As described previously this can correspond to a large waste of money,time, and resources.

The mask 106 of FIG. 8 does not suffer these drawbacks. Because theouter lateral surfaces or sidewalls of the absorption layer 118 of themask 106 are covered by the photoresist 128 during the plasma etchingprocess of FIG. 7, the surface voltage of the absorption layer 118 isstable. Because the surface voltage of the absorption layer is stable,the etching rate of the absorption layer 118 is constant at all exposedlocations of the absorption layer 118. Furthermore, semiconductor wafersprocessed with the mask 106 will not suffer the defects that may besuffered by semiconductor wafers processed with the mask 140 of FIG. 9.

FIG. 10 is a flow diagram of a method 1000 for forming an extremeultraviolet photolithography mask, according to one embodiment. At 1002the method 1100 includes forming, on a substrate, a reflectivemultilayer configured to reflect ultraviolet radiation during extremeultraviolet photolithography processes. One example of a substrate isthe substrate 112 of FIG. 2. One example of a reflective multilayer isthe reflective multilayer 114 of FIG. 2. At 1004 the method 1000includes forming a buffer layer on the reflective multilayer. Oneexample of a buffer layer is the buffer layer 116 of FIG. 2. At 1006 themethod 1000 includes forming an absorption layer on the buffer layer andhaving a lateral width that is less than a lateral width of the bufferlayer, wherein the absorption layer is configured to absorb ultravioletlight during extreme ultraviolet photolithography processes. One exampleof an absorption layer is the absorption layer 118 of FIG. 2.

FIG. 11 is a flow diagram of a method 1100 for forming an extremeultraviolet photolithography mask, according to one embodiment. At 1102the method 1100 includes forming, on a substrate, a reflectivemultilayer configured to reflect ultraviolet light during extremeultraviolet photolithography processes. One example of a substrate isthe substrate 112 of FIG. 2. One example of a reflective multilayer isthe reflective multilayer 114 of FIG. 2. At 1104 the method 1100includes forming a buffer layer on the reflective multilayer. Oneexample of a buffer layer is the buffer layer 116 of FIG. 2. At 1106 themethod 1100 includes forming an absorption layer on the buffer layer,wherein the absorption layer is configured to absorb ultraviolet lightduring extreme ultraviolet photolithography processes. One example of anabsorption layer is the absorption layer 118 of FIG. 2. At 1108 themethod 1100 includes exposing an outer portion of a top surface of thebuffer layer by removing an outer portion of the absorption layer with afirst etching process. At 1110 the method includes forming trenches inthe absorption layer with a second etching process.

In one embodiment an extreme ultraviolet photolithography mask includesa substrate and a reflective multilayer positioned on the substrate andconfigured to reflect ultraviolet radiation during extreme ultravioletphotolithography processes. The mask includes a buffer layer positionedon the reflective multilayer and an absorption layer positioned on thebuffer layer and configured to absorb ultraviolet light during extremeultraviolet photolithography processes. At least one outer edge of theabsorption layer is separated laterally from a corresponding outer edgeof the buffer layer such that a peripheral portion of a top surface ofthe buffer layer is exposed.

In one embodiment a method includes forming, on a substrate, areflective multilayer configured to reflect ultraviolet radiation duringextreme ultraviolet photolithography processes. The method includesforming a buffer layer on the reflective multilayer. The method includesforming an absorption layer on the buffer layer and having a lateralwidth that is less than a lateral width of the buffer layer. Theabsorption layer is configured to absorb ultraviolet light duringextreme ultraviolet photolithography processes.

In one embodiment a method includes forming, on a substrate, areflective multilayer configured to reflect ultraviolet light duringextreme ultraviolet photolithography processes. The method includesforming a buffer layer on the reflective multilayer and forming anabsorption layer on the buffer layer. The absorption layer is configuredto absorb ultraviolet light during extreme ultraviolet photolithographyprocesses. The method includes exposing an outer portion of a topsurface of the buffer layer by removing an outer portion of theabsorption layer with a first etching process. The method includesforming trenches in the absorption layer with a second etching process.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary, to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. An extreme ultraviolet photolithography mask comprising: a substrate;a reflective multilayer positioned on the substrate and configured toreflect ultraviolet radiation during extreme ultravioletphotolithography processes; a buffer layer positioned on the reflectivemultilayer; an absorption layer positioned on the buffer layer andconfigured to absorb ultraviolet light during extreme ultravioletphotolithography processes, wherein at least one outer edge of theabsorption layer is separated laterally from a corresponding outer edgeof the buffer layer such that a peripheral portion of a top surface ofthe buffer layer is exposed.
 2. The extreme ultraviolet photolithographymask of claim 1, wherein the at least one outer edge of the absorptionlayer is separated laterally from the corresponding outer edge of thebuffer layer by 0.2 mm to 2 mm.
 3. The extreme ultravioletphotolithography mask of claim 1, wherein the absorption layer includesa plurality of trenches exposing the top surface of the buffer layer. 4.The extreme ultraviolet photolithography mask of claim 1, wherein thebuffer layer includes ruthenium.
 5. The extreme ultravioletphotolithography mask of claim 1, wherein the absorption layer includestantalum.
 6. The extreme ultraviolet photolithography mask of claim 1,wherein a lateral width of the absorption layer is less than a lateralwidth of the buffer layer along a same direction.
 7. The extremeultraviolet photolithography mask of claim 1, wherein the reflectivemultilayer includes a plurality of pairs of layers configured tocollectively reflect ultraviolet radiation during extreme ultravioletphotolithography processes.
 8. A method, comprising: forming, on asubstrate, a reflective multilayer configured to reflect ultravioletradiation during extreme ultraviolet photolithography processes; forminga buffer layer on the reflective multilayer; and forming an absorptionlayer on the buffer layer and having a lateral width that is less than alateral width of the buffer layer along a same direction, wherein theabsorption layer is configured to absorb ultraviolet light duringextreme ultraviolet photolithography processes.
 9. The method of claim8, wherein forming the absorption layer includes: depositing theabsorption layer on the buffer layer; and exposing an outer perimeter ofa top surface of the buffer layer by removing an outer portion of theabsorption layer.
 10. The method of claim 8, further comprising:depositing photoresist on top of the absorption layer, on sidewalls ofthe absorption layer, and on an out perimeter of the top surface of thebuffer layer; patterning the photoresist; and forming trenches in theabsorption layer by performing a plasma etch while the photoresist iscovering the sidewalls of the absorption layer.
 11. The method of claim10, wherein the plasma etch includes a chlorine gas.
 12. The method ofclaim 10, wherein the plasma etch selectively etches the absorptionlayer at a faster rate than the buffer layer.
 13. The method of claim 8,wherein the substrate includes silicon dioxide.
 14. The method of claim8, wherein the reflective multilayer includes a plurality of pairs oflayers configured to collectively reflect ultraviolet light duringextreme ultraviolet photolithography processes.
 15. A method,comprising: forming, on a substrate, a reflective multilayer configuredto reflect ultraviolet light during extreme ultraviolet photolithographyprocesses; forming a buffer layer on the reflective multilayer; formingan absorption layer on the buffer layer, wherein the absorption layer isconfigured to absorb ultraviolet light during extreme ultravioletphotolithography processes; exposing an outer portion of a top surfaceof the buffer layer by removing an outer portion of the absorption layerwith a first etching process; and forming trenches in the absorptionlayer with a second etching process.
 16. The method of claim 15, furthercomprising: covering sidewalls of the absorption layer with photoresistafter the first etching process; and performing the second etchingprocess while the photoresist covers the sidewalls of the absorptionlayer.
 17. The method of claim 16, wherein covering the sidewalls of theabsorption layer with photoresist includes covering the outer portion ofthe top surface of the buffer layer with photo resist.
 18. The method ofclaim 15, wherein the second etching process selectively etches theabsorption layer at a faster rate than the buffer layer.
 19. The methodof claim 15, wherein the second etching process is a plasma etchingprocess.
 20. The method of claim 19, wherein the plasma etching processincludes etching the absorption layer with a chlorine gas.